Autofocus issue with Sigma 10-20mm? Help!

Started Jan 15, 2014 | Discussions thread
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banflu New Member • Posts: 12
Autofocus issue with Sigma 10-20mm? Help!

Hi everyone,

Been lurking for a while but finally registered here as I ran into a problem!

I bought a Nikon D5100 a few months ago (my first DSLR) and after a while I noticed that I really started to like wide angle photos so I also bought a Sigma 10-20mm f3.5 lens. From the start I had a feeling that it's autofocus wasn't 100%, but at first I thought nothing of it - I am only a beginner after all.

But recently I was on holiday so I used the camera (and this Sigma lens) quite a lot .. and I've had quite a number of out-of-focus photos. I later realised that they are never out-of-focus if I use live view. Of course, live view is much slower so it is quite an issue.

Anyway, after making extensive testing I came to the conclusion that the Sigma lens is to blame. Please take a look at this video:

In this test I placed the camera on a small tripod (gorilla pod) and attached a focus test chart on the wall. I focused on the chart multiple times using live view. It always focussed perfectly - any photo i take in live view is 100% in focus. Later I put it out of live view, and the focus setting is visibly different in the focus window on the lens. Also, the focussing is inconsistent when not in live view. Put it back to live view and it becomes 100% consistent and perfect.

I later tried this same test with a Nikkor prime 50mm lens, and it worked perfect - the focus is always exactly the same, both in live view and in normal view.

Any thoughts? Has anyone else had a similar issue? The lens is still under warranty ... should I try to get a replacement, or should I fork out more $$$ and get a Nikkor 10-24mm?

Many thanks in advance for your help!

Nikon D5100 Sigma 10-20mm F3.5 EX DC HSM
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